Display screen or portion thereof with transitional graphical user interface



FIG. 1 is a front view of the first image in a sequence for a display screen or portion thereof with transitional graphical user interface showing our new design;

FIG. 2 is the second image thereof;

FIG. 3 is the third image thereof;

FIG. 4 is the fourth image thereof;

FIG. 5 is the fifth image thereof; and,

FIG. 6 is the sixth image thereof.

The dashed broken line perimeter in the drawings illustrates a display screen or portion thereof and forms no part of the claimed design. The remaining dashed broken lines in the drawings illustrate portions of the transitional graphical user interface that form no part of the claimed design.

The appearance of the graphical user interface transitions sequentially between the images shown. The process or period in which one image transitions to another forms no part of the claimed design. 

CLAIM The ornamental design for a display screen or portion thereof with transitional graphical user interface, as shown and described. 